Flexible insulated air duct may include a core of a wire helix encapsulated in plastic film duct liner, glass wool insulation wrapped around the core, and a plastic film sleeve over the insulation. Duct length may be as long as twenty-five feet. Before this invention, the glass wool used was of the type produced by the apparatus disclosed in U.S. Pat. No. 3,865,566, issued Feb. 11, 1975. That is, because twenty-five feet of the wool had to be pulled from the roll each time, it was thought best to use wool having glass fibers oriented mainly longitudinally of the batt, for greater strength and less pulling apart. In actual practice, fiberizing apparatus of the type shown in the above patent includes only two or three spinners, and glass throughput and conveyor speed are relatively low. Therefore, the wool batts with longitudinally oriented glass fibers are relatively expensive. Even so, before this invention, it was not thought that wool batts with randomly oriented fibers would be strong enough not to pull apart when twenty-five or more feet were pulled off a roll.
Glass wool batts with randomly oriented glass fibers are made by apparatus such as disclosed in U.S. Pat. No. 3,523,774, issued Aug. 11, 1970. In actual practice, such fiberizing apparatus has a large number of spinners in order that relatively thick blankets of building insulation can be made at relatively high conveyor speeds. These conveyor speeds are already so high that it is impractical to attempt to run the conveyor at even higher speeds to produce relatively thin glass wool batts for flexible insulated air duct. The solution was to split the blanket or batt. Thus, for example, it is practical to make a batt nominally three inches thick and to split it into two batts of one and one-half inch thickness before roll-up. The apparatus of this invention is designed for use of such "two batts in one roll" supply rolls in the manufacture of flexible insulated air duct.